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Entry  Thu Aug 1 03:34:35 2013, Chloe, DailyProgress, ECDL, Assembling ECDL 
    Reply  Thu Aug 1 18:33:12 2013, Chloe, DailyProgress, ECDL, Assembling ECDL tempsensor.PNG
       Reply  Fri Aug 2 18:15:06 2013, Chloe, DailyProgress, ECDL, Assembling ECDL possible_tec_mount.PNG
          Reply  Mon Aug 5 18:47:04 2013, Chloe, DailyProgress, ECDL, Assembling ECDL heating.PNGcooling.PNGnoise_beginning.JPG
             Reply  Tue Aug 6 19:48:19 2013, Chloe, DailyProgress, ECDL, Assembling ECDL 100_0079.JPG
                Reply  Wed Aug 7 18:13:21 2013, Chloe, DailyProgress, ECDL, Assembling ECDL 
                   Reply  Thu Aug 8 18:43:44 2013, Chloe, DailyProgress, ECDL, Assembling ECDL 100_0081.JPGcool_bridge.PNGheat_bridge.PNG
                      Reply  Fri Aug 9 18:01:47 2013, Chloe, DailyProgress, ECDL, Assembling ECDL cool_bridge2.PNGheat_bridge2.PNG
                         Reply  Tue Aug 13 18:13:35 2013, Chloe, DailyProgress, ECDL, Assembling ECDL 
                            Reply  Thu Aug 15 18:53:45 2013, Chloe, DailyProgress, ECDL, Assembling ECDL 100_0104.JPG
Message ID: 1289     Entry time: Thu Aug 8 18:43:44 2013     In reply to: 1285     Reply to this: 1292
Author: Chloe 
Type: DailyProgress 
Category: ECDL 
Subject: Assembling ECDL 

 Today I designed a better circuit to measure the TEC's response with the oscilloscope. It is called a bridge circuit, and allows for the output voltage to be centered around 0 instead. This type of circuit is often used for different sensors, and seems to fit our purposes well here. The schematic is attached here. 

100_0081.JPG

After I built this circuit (modified the circuit I was previously using), I tested it with the TEC to see how the PID gain calibration looked. This took awhile to get a signal, because it seems like the oscilloscope I was using had some problems. I took data of heating and cooling shown below (didn't bother converting to temperature since we're mostly interested in how the temperature or voltage settles right now). 

cool_bridge.PNG

heat_bridge.PNG

A lot of the data I tried to take today had the same sort of oscillations as for the cooling data shown above (about 0.04 Hz). However, I didn't see such oscillations when I hooked the circuit up to a multimeter and monitored the voltage changes over time. In fact, the voltmeter suggested that the voltage stabilized much more quickly. I'm going to look at this again tomorrow to see if I can figure out the cause of these oscillations, and perhaps tune the PID gain on the TEC better now that I can see how the temperature settles much more easily and quantitatively. 


Today, I also finalized the Solidworks drawings for the insulator that will be used to thermally isolate the laser diode from the rest of the setup, as well as the heat sink that will be in contact with the Peltier element. These files are on the SVN, and I will try to go to the machine shop with these soon. I should have done this earlier. 

I will be presenting my project at the end of August, so Tara wants me to put together a talk so we can rehearse next week. I am going to start doing this in my free time. 

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